Reuters: A period of global warming contributed to the rise of the Inca empire, allowing it to increase food production by planting at higher altitudes on farmland irrigated with water from melting glaciers, a team of European and American scientists say. The rise of the Inca empire — which was centered in what is now Peru and reached into present-day Colombia, Ecuador, Chile and Bolivia — usually is attributed to sophisticated organization, a large labor force and a big army. But new …